U.S. patent application number 14/734522 was filed with the patent office on 2016-12-15 for helium enhanced heat transfer in adsorptive liquid argon purification process.
The applicant listed for this patent is Hai Du, Steven R. Falta, Scot E. Jaynes, Neil A. Stephenson. Invention is credited to Hai Du, Steven R. Falta, Scot E. Jaynes, Neil A. Stephenson.
Application Number | 20160362298 14/734522 |
Document ID | / |
Family ID | 56027244 |
Filed Date | 2016-12-15 |
United States Patent
Application |
20160362298 |
Kind Code |
A1 |
Du; Hai ; et al. |
December 15, 2016 |
HELIUM ENHANCED HEAT TRANSFER IN ADSORPTIVE LIQUID ARGON
PURIFICATION PROCESS
Abstract
The present invention generally relates to a method to enhance
heat transfer in the temperature swing adsorption process (TSA) and
to an intensified TSA process for gas/liquid purification or bulk
separation. Helium is designed as the heat carrier media to
directly bring heat/cool to the adsorbent bed during the TSA
cycling process. With helium's superior heat conductivity, the time
consuming regeneration steps (warming, regeneration and precooling)
of TSA process can be significantly reduced and allowing for the
TSA process to be intensified.
Inventors: |
Du; Hai; (East Amherst,
NY) ; Jaynes; Scot E.; (Lockport, NY) ; Falta;
Steven R.; (Honeoye Falls, NY) ; Stephenson; Neil
A.; (East Amherst, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Du; Hai
Jaynes; Scot E.
Falta; Steven R.
Stephenson; Neil A. |
East Amherst
Lockport
Honeoye Falls
East Amherst |
NY
NY
NY
NY |
US
US
US
US |
|
|
Family ID: |
56027244 |
Appl. No.: |
14/734522 |
Filed: |
June 9, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 53/0462 20130101;
C01B 2210/0045 20130101; C01B 23/0078 20130101; F25J 3/08 20130101;
B01D 2256/18 20130101; B01D 2257/102 20130101; B01D 2257/104
20130101; B01D 2259/402 20130101; F25J 2205/64 20130101; F25J
3/04775 20130101; C01B 2210/0034 20130101; B01D 53/0438
20130101 |
International
Class: |
C01B 23/00 20060101
C01B023/00; F25J 3/08 20060101 F25J003/08; F25J 3/04 20060101
F25J003/04; B01D 53/04 20060101 B01D053/04 |
Claims
1. A method of intensifying a temperature swing adsorption process
which comprises at least one adsorbent bed, wherein said method
comprises maintaining said adsorbent bed in an environment of at
least one heat transfer gas during the cooling of said adsorbent
bed to cryogenic temperatures, wherein said heat transfer gas has a
thermal conductivity value greater than or equal to 2.0 mW/m K
measured at a temperature of 100K.
2. The method of claim 1 wherein said at least one heat transfer
gas accelerates the cooling of said at least one adsorbent bed
through conductive heat transfer, convective heat transfer, or both
conductive and convective heat transfer.
3. The method of claim 1 wherein said at least one heat transfer
gas comprises at least one of helium, hydrogen, neon, krypton,
xenon, or combinations and mixtures thereof.
4. The method of claim 1 wherein said heat transfer gas comprises
helium.
5. The method of claim 1 wherein said adsorbent bed is located in
an adsorbent vessel comprising an outer jacket for cooling media
and an inner vessel containing said adsorbent bed, wherein said
cooling media indirectly cools down the adsorbent bed in said inner
vessel, wherein helium is loaded into said inner vessel in an
amount effective to substantially fill the void space of said inner
vessel during the indirect cooling of said adsorbent bed.
6. The method of claim 5 wherein the cooling media in said outer
jacket is liquid nitrogen.
7. The method of claim 1 wherein said temperature swing adsorption
process is a liquid argon purification process or a gas phase argon
purification process, and the impurity to be removed is oxygen or
nitrogen or both oxygen and nitrogen.
8. The method of claim 1 wherein said adsorption process is
conducted at a pressure of from about -5 to about 350 psig.
9. The method of claim 1 wherein said adsorption process is
conducted at a pressure of from about 2 to about 75 psig.
10. A temperature swing adsorption process for purifying a liquid
feed stream comprising at least one impurity, said process
comprising: a) supplying said liquid feed to the inlet of an
adsorbent vessel containing an adsorbent bed, wherein said
adsorbent vessel contains an inlet and an outlet and is configured
for indirect and direct cooling, b) adsorbing at least part of said
at least one impurity on the adsorbent in said bed thereby
producing a purified liquid product leaving said adsorbent bed from
the outlet of said adsorbent vessel with less impurity than present
in said liquid feed at the inlet of said adsorbent vessel; c)
removing residual liquid from said adsorbent bed, optionally by
introducing a displacement purge gas; d) warming said adsorbent bed
containing said adsorbent to a temperature, effective to desorb at
least part of the adsorbed impurity and removing said adsorbed
impurity from the adsorbent bed such that the liquid feed may be
supplied for purposes of repeating the cycle; e) loading at least
one inert heat transfer gas into the adsorbent vessel in an amount
effective to substantially fill the void space of the adsorbent bed
and at a pressure effective to maintain the adsorbent bed at
positive pressure during the indirect cooling thereof; f)
optionally indirectly cooling said adsorbent bed to a temperature
sufficient to maintain the liquid feed in a liquid phase; g)
directly cooling said adsorbent bed to a temperature such that said
adsorbent bed sustains the liquid feed in a liquid phase; h)
wherein said process steps (a)-(g) are repeated in a cyclical
manner.
11. The process of claim 10 wherein said adsorbent vessel comprises
an outer jacket for cooling media and an inner vessel containing
said adsorbent bed, wherein a cooling media is maintained in said
outer jacket in order to indirectly cool down the adsorbent in said
inner vessel.
12. The process of claim 11 wherein the inert heat transfer gas is
specified to the particular purification or separation process and
comprises at least one of helium, hydrogen, neon, krypton, xenon,
or combinations thereof.
13. The process of claim 11 wherein helium is the heat transfer gas
and liquid nitrogen is the cooling media.
14. The process of claim 10 wherein said liquid feed stream is
selected from oxygen, nitrogen, carbon monoxide, methane, argon,
helium, neon, krypton, and xenon.
15. The process of claim 14 wherein said feed stream is argon and
said impurity is oxygen, nitrogen, or both oxygen and nitrogen.
16. An adsorption process for purifying a feed stream that
comprises liquid argon and oxygen, said process comprising: a)
supplying a liquid argon feed that contains oxygen to the inlet of
an adsorbent vessel containing an adsorbent bed, wherein said
adsorbent vessel contains an inlet and an outlet and is configured
for indirect and direct cooling, adsorbing at least part of the
oxygen on the adsorbent in said bed thereby producing a purified
liquid argon product leaving said adsorbent bed from the outlet of
said adsorbent vessel with less oxygen than present in said liquid
argon feed at the inlet of said adsorbent vessel; b) draining
residual liquid argon from said adsorbent bed, optionally by
introducing a displacement purge gas; c) allowing said adsorbent
bed containing said adsorbent to warm to a temperature sufficient
to desorb at least part of the adsorbed oxygen and removing said
adsorbed oxygen from the adsorbent bed such that the liquid argon
feed may be supplied for purposes of repeating the cycle; d)
loading helium into the adsorbent vessel in an amount effective to
substantially fill the void space of the adsorbent bed and at a
pressure effective to maintain the adsorbent bed at positive
pressure during indirect cooling; e) indirectly cooling said
adsorbent bed to a temperature of less than about 150 degrees
Kelvin using liquid nitrogen; f) directly cooling said adsorbent
bed with purified liquid argon and/or cold helium to a temperature
sufficient to sustain the argon feed in a liquid phase; g) wherein
said process steps (a)-(f) are repeated in a cyclical manner.
17. The process of claim 16, wherein the liquid argon feed for step
(a) contains more than 10 parts per million of oxygen and less or
equal to 50,000 parts per million of oxygen and wherein removal of
said oxygen from said liquid argon feed results in a purified
liquid argon product with less than or equal to 10 parts per
million of oxygen.
18. The process of claim 16, wherein in step (b) the displacement
purge gas comprises nitrogen, or argon, or helium or a combination
or mixture thereof.
19. The process of claim 16, further comprising a second adsorbent
bed wherein in one mode of operation said second adsorbent bed is
operated such that it is purifying liquid argon feed in step (a)
while the first adsorbent bed is being regenerated and
correspondingly the second adsorbed bed is regenerated while said
first adsorbent bed is purifying the liquid argon feed in step (a),
so as to produce a purified liquid argon product stream
continuously, and in another operation mode said second adsorbent
bed and said first adsorbent bed are operated to purify liquid
argon feed in step (a) to produce a purified liquid argon product
stream.
20. The process of claim 19, further comprising two or more
adsorbent beds, wherein the process for purifying liquid argon in
each bed is offset from one another.
21. A temperature swing adsorption process for purifying a liquid
argon feed stream comprising at least one impurity, said process
comprising: a) supplying said liquid argon feed stream to the inlet
of an adsorbent vessel comprising an adsorbent bed, wherein said
vessel contains an inlet and outlet and is configured for direct
cooling, b) adsorbing at least part of said impurity on the
adsorbent thereby producing a purified liquid argon product leaving
said adsorbent bed from the outlet of said adsorbent vessel; b)
draining from the outlet or inlet of said adsorbent bed residual
liquid argon, optionally by introducing a displacement purge gas to
the inlet or outlet of said adsorbent vessel while maintaining the
adsorbent bed at temperature below 120 K; c) supplying a helium
purge at the inlet or outlet of the adsorbent bed and allowing said
adsorbent bed containing said adsorbent to warm to a temperature
sufficient to desorb at least part of the adsorbed impurity and
removing same from the outlet or inlet of said adsorbent bed,
wherein said helium purge is maintained until the gaseous effluent
exiting the inlet side of said adsorbent bed is predominantly
helium, and; d) directly cooling said adsorbent bed with cold
helium to a temperature sufficient to maintain argon in liquid
form, wherein said cold helium is maintained at a positive pressure
in said adsorbent vessel during the direct cooling of said
adsorbent bed; e) wherein said process steps (a)-(d) are repeated
in a cyclical manner.
22. The process of claim 21, wherein the impurity comprises oxygen,
nitrogen or both oxygen and nitrogen.
23. The process of claim 21 wherein the liquid argon feed for step
(a) contains more than 10 parts per million of oxygen and less or
equal to 40,000 parts per million of oxygen and wherein removal of
said oxygen from said liquid argon feed results in a purified
liquid argon product with less than or equal to 10 parts per
million of oxygen.
24. The process of claim 21, wherein the liquid argon feed for step
(a) contains more than 10 parts per million of oxygen and less or
equal to 40,000 parts per million of oxygen and wherein removal of
said oxygen from said liquid argon feed results in a purified
liquid argon product with less or equal to 1 part per million of
oxygen.
25. The process of claim 21, wherein the residual liquid argon is
drained from the adsorbent bed in step (b) using a displacement
purge gas comprising nitrogen, or argon, or helium or a combination
or mixture thereof.
26. The process of claim 21, wherein a warm nitrogen purge step
precedes the warm helium purge of step (c), and the warming of the
adsorbent bed in step is continued until the adsorbent bed reaches
a temperature of at least 200 degrees Kelvin.
27. The process of claim 21, further comprising a second adsorbent
bed wherein in one mode of operation said second adsorbent bed is
operated such that it is purifying liquid argon feed in step (a)
while the first adsorbent bed is being regenerated and
correspondingly the second adsorbed bed is regenerated while said
first adsorbent bed is purifying the liquid argon feed in step (a),
so as to produce a purified liquid argon product stream
continuously, and in another operation mode said second adsorbent
bed and said first adsorbent bed are operated to purify liquid
argon feed in step (a) to produce a purified liquid argon product
stream.
28. The process of claim 21, further comprising two or more
adsorbent beds, wherein the process for purifying liquid argon in
each bed is offset from one another.
29. A temperature swing adsorption process for purifying a gas
phase feed stream comprising at least one impurity, said process
comprising: a) supplying said gas phase feed to the inlet of an
adsorbent vessel containing an adsorbent bed, wherein said
adsorbent vessel contains an inlet and an outlet and is configured
for indirect and direct cooling, b) adsorbing at least part of said
at least one impurity on the adsorbent in said bed thereby
producing a purified gas phase product leaving said adsorbent bed
from the outlet of said adsorbent vessel with less impurity than
present in said gas phase feed at the inlet of said adsorbent
vessel; c) warming said adsorbent bed containing said adsorbent to
a temperature, effective to desorb at least part of the adsorbed
impurity and removing said adsorbed impurity from the adsorbent bed
optionally by introducing a displacement purge gas to the inlet or
outlet of said adsorbent vessel such that the gas phase feed may be
supplied for purposes of repeating the cycle; d) loading at least
one inert heat transfer gas into the adsorbent vessel in an amount
effective to substantially fill the void space of the adsorbent bed
and at a pressure effective to maintain the adsorbent bed at
positive pressure during the indirect cooling thereof; e)
optionally indirectly cooling said adsorbent bed to a temperature
of less than about 150 degrees Kelvin; f) directly cooling said
adsorbent bed to a temperature of less than about 150 degrees
Kelvin; g) wherein said process steps (a)-(f) are repeated in a
cyclical manner.
30. The process of claim 29 wherein said adsorbent vessel comprises
an outer jacket for cooling media and an inner vessel containing
said adsorbent bed, wherein a cooling media is maintained in said
outer jacket in order to indirectly cool down the adsorbent in said
inner vessel.
31. The process of claim 30 wherein the inert heat transfer gas is
specified to the particular purification or separation process and
comprises at least one of helium, hydrogen, neon, krypton, xenon,
or combinations thereof.
32. The process of claim 29 wherein helium is the heat transfer gas
and liquid nitrogen is the cooling media.
33. The process of claim 29 wherein said gas phase feed stream is
selected from oxygen, nitrogen, carbon monoxide, methane, argon,
helium, neon, krypton, and xenon.
34. The process of claim 29 wherein said feed stream is argon and
said impurity is oxygen, nitrogen, or both oxygen and nitrogen.
35. The process of claim 34, wherein the gas phase argon feed for
step (a) contains from about 10 parts per million to about 50,000
parts per million of oxygen and wherein removal of said oxygen from
said argon feed results in a purified argon product with less than
or equal to 10 parts per million of oxygen.
36. The process of claim 29, wherein in step (c) the displacement
purge gas comprises nitrogen, or helium or a combination or mixture
thereof.
37. The process of claim 29, further comprising a second adsorbent
bed wherein in one mode of operation said second adsorbent bed is
operated such that it is purifying argon feed in step (a) while the
first adsorbent bed is being regenerated and correspondingly the
second adsorbed bed is regenerated while said first adsorbent bed
is purifying the argon feed in step (a), so as to produce a
purified argon product stream continuously, and in another
operation mode said second adsorbent bed and said first adsorbent
bed are operated to purify argon feed in step (a) to produce a
purified argon product stream.
38. The process of claim 37, further comprising two or more
adsorbent beds, wherein the process for purifying argon in each bed
is offset from one another.
39. The process of claim 1 wherein said temperature swing
adsorption process is a purification process for the purification
of a liquid or gas phase feed stream selected from oxygen,
nitrogen, carbon monoxide, methane, argon, helium, neon, krypton,
and xenon.
40. The process of claim 29 wherein the displacement purge gas is
introduced into said adsorbent vessel while maintaining the
adsorbent bed at a temperature of from about 90-150 degrees Kelvin
and a pressure of about 15 psig.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method to enhance heat
transfer in a temperature swing adsorption process (TSA) and to an
intensified TSA process for gas/liquid purification or bulk
separation.
DESCRIPTION OF RELATED ART
[0002] Temperature swing adsorption ("TSA") processes are based on
the periodic variation of the temperature of an adsorbent bed and
are widely used in gas/liquid purification or bulk separation. The
adsorption occurs at a lower temperature and the bed is regenerated
at a higher temperature. TSA processes are commonly used for trace
impurity removal from air in pre-purification systems as well as
abatement of volatile organic compounds from process gas
streams.
[0003] The adsorption of gases onto an adsorbent is an exothermic
process, i.e., the temperature of an adsorbent will rise during the
course of an adsorption process because of the heat given off
during the adsorption. The quantity of heat given off is directly
proportional to the amount adsorbed, and depends on several factors
including concentration in the gas mixture of the component that is
being adsorbed: the more impurity adsorbed from a gas/liquid stream
the greater the amount of heat given off during the adsorption step
and the greater the temperature rise.
[0004] In most gas/liquid adsorption processes the adsorption
efficiency is inversely proportional to the temperature at which
the adsorption is conducted. The ability of an adsorbent to adsorb
a given impurity generally diminishes as the temperature of the
adsorption bed increases. Because of this it is usually desirable
to conduct the adsorption at a low temperature, and to minimize any
increase in bed temperature as the adsorption proceeds.
[0005] The problem of temperature rise can be particularly acute
when, for the purpose of maintaining product purity specifications
it is necessary to conduct an adsorption process at just above the
dew point of the gas mixture, and even a small increase in bed
temperature will cause the product to fail to meet purity
requirements. In such cases it is often necessary to reduce the
concentration of the impurity to be adsorbed as much as possible by
other techniques prior to the adsorption procedure and to apply
cooling to the bed to maintain it at constant temperature during
adsorption.
[0006] The key steps in a TSA cycle process are adsorption
(purification) to make product, warming (purge) the adsorbent bed
to regenerate the adsorbent, and pre-cooling the adsorbent bed for
next cycle. TSA cycle times are usually quite long due in part to
the poor heat conductivity of most adsorbents, leading to high
energy consumption and large amounts of adsorbent needed. As a
result, there is considerable interest in the field focused on
intensifying the TSA process to overcome the above mentioned
disadvantages. Most of the studies are focusing on the adsorbent
vessel design to increase heat conduction between the adsorbent and
the heat transfer media. For example, shell and tube heat exchanger
type adsorbent vessel is proposed in EP1291067 aiming to intensify
the TSA process. Others' proposed different vessel configurations
to enhance the heat conduction during TSA process. Those designs
are complex and significantly increase the TSA process capital
costs.
[0007] In the cryogenic liquid purification area, purification is
conducted under cryogenic temperatures, and the adsorbent is
regenerated at higher temperatures. After regeneration the
adsorbent bed is pre-cooled down to cryogenic temperatures for the
next purification cycle. Typically in the current art, the
adsorbent in the vessel is directly cooled by either a cold product
stream or cold crude (impurity containing) feed stream. However,
since the adsorption capacity of the adsorbent is high at cryogenic
temperatures, precooling with a direct flow stream, i.e., direct
cooling, is normally avoided due to the parasitic loading of the
coolant on the adsorbent, which diminishes the adsorbent's capacity
to remove the impurities from the feed stream being purified. In
order to compensate for the capacity loss during cooling many
systems are overdesigned, leading to increased capital
expenditures. With indirect cooling, the vessel is typically
designed with a jacket around the adsorbent bed and uses cooling
media in the jacket to indirectly cool down the adsorbent in the
inner vessel. Direct contact between the cooling media and the
adsorbent is therefore avoided. However, during the indirect
cooling step, any gas residue molecules left from previous purge
step are adsorbed onto the adsorbent, which can create a vacuum
environment inside the inner adsorbent vessel. This vacuum requires
the appropriate vessel design to ensure structural integrity, and
all valves and connections represent potential leak points. The
vacuum created in the inner adsorbent vessel during the indirect
cooling also reduces the heat transfer to a large extent.
Therefore, from vessel design standpoint, a heat exchange type
vessel with small adsorbent vessel diameter is required and
significant time is needed to indirectly cool down the adsorbent in
the inner vessel. These drawbacks place limits on vessel design for
intermediate and large plants, affect the overall capacity of the
TSA purifier, and add significant costs to design and operating
reliability.
[0008] U.S. patent application 2014/0245781, which is incorporated
herein in its entirety by reference, discloses an adsorptive liquid
argon (LAR) purification process using a temperature swing
adsorption (TSA) cycling from 90K to ambient temperature that
removes 10-10,000 ppm O.sub.2 from a liquid argon stream. The bed
after regeneration is subjected to an indirect cooling step to a
specified temperature, at least 150K, prior to bringing the
cryogenic liquid in direct contact with the adsorbent, which is
important to control the micro structure of the adsorbent and
ensure that the capacity of the bed to remove O.sub.2 is maximized.
The indirect cooling step is, however, a time limiting step due to
the poor heat conductivity of adsorbent bed, which constrains
process cycle time and restricts process intensification. The
indirect cooling time increases with increasing adsorbent vessel
diameter and becomes an important consideration to ensure cooling
of the inner of adsorbent bed by heat transfer to the jacket. Also,
during the indirect cooling step, a vacuum is formed inside the
vessel as the gas molecules left in adsorbent vessel from prior
purging steps are adsorbed onto the adsorbent.
[0009] The present invention seeks to alleviate the aforementioned
deficiencies by providing a method to enhance heat transfer in the
temperature swing adsorption process (TSA) and an intensified TSA
process for gas/liquid purification or bulk separation. Other
objects and aspects of the present disclosure will become apparent
to one of ordinary skill in the art upon review of the
specification, drawings, and claims appended hereto.
SUMMARY OF THE INVENTION
[0010] The present invention generally relates to a method to
enhance heat transfer in the temperature swing adsorption process
(TSA) and to an intensified TSA process for gas/liquid purification
or bulk separation. Helium is designed as the heat carrier
media/transfer gas to directly bring heat/cool to the adsorbent bed
during the TSA cycling process. With helium's superior heat
conductivity, the time consuming regeneration steps (warming,
regeneration and precooling) of TSA process can be significantly
reduced and allowing for the TSA process to be intensified.
BRIEF DESCRIPTION OF THE FIGURES
[0011] The objectives and advantages of the invention will be
better understood from the following detailed description of the
preferred embodiments thereof in connection with the accompanying
figure wherein like numbers denote the same features
throughout.
[0012] FIG. 1 illustrates an adsorptive LAR purification process
with indirect cooling.
[0013] FIG. 2a illustrates a helium enhanced TSA process for LAR
purification
[0014] FIG. 2h illustrates a helium enhanced TSA process for LAR
purification with waste nitrogen purge.
[0015] FIG. 3 illustrates the steps for a cyclic TSA process as
provided in the exemplary embodiments of the present invention.
[0016] FIG. 4 depicts an experimental system for heat transfer
measurement in packed bed, wherein P: pressure transducer, F: mass
flow meter, T1-T3: thermocouples.
[0017] FIG. 5 shows the experimental results of cooling down an
adsorbent bed at different conditions with a vessel internal
diameter (ID) of 5.3 inches.
[0018] FIGS. 6a and 6b illustrate the cooling down of adsorbent bed
at different thermal conductivity and vessel diameters of 13.5
inches and 17.5 inches.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The invention relates to a method for enhancing heat
transfer in a TSA process and to an intensified TSA process for
gas/liquid purification or bulk separation. The intensified TSA
process of the invention can be used to purify any gas which can be
liquefied at the temperature at which it is desired to conduct the
adsorption process and is applicable to methods and systems that
heat and/or cool directly and/or indirectly.
[0020] In one embodiment the process of the invention is
advantageously utilized to purify a permanent gas, i.e., a gas that
cannot be condensed by pressure alone, by removing one or more
permanent gas impurities therefrom. Included among the permanent
gases are oxygen, nitrogen, carbon monoxide, methane, and the noble
gases, for example, argon, helium, neon, krypton, xenon, and the
like.
[0021] In the method of the present invention a heat transfer
carrier gas is utilized to decrease the indirect and/or direct
cooling time necessary in cyclic adsorption processes, thus
intensifying the TSA process. For example, in the removal of oxygen
required for the purification of liquid argon, the heat transfer
carrier gas works as the heat transfer media to accelerate the
cooling process and parts per million concentration levels of
impurities of oxygen can be removed from a liquid argon feed stream
efficiently and economically. This purification process can be
integrated with an air separation plant or unit (ASU), under field
service relevant conditions.
[0022] The heat transfer carrier gas or heat transfer gas employed
in the embodiments of the invention improves thermal conductivity
in the direct and/or indirect cooling of an adsorbent bed during
the TSA cycling process. Thermal conductivity is the property of a
material or gas to conduct heat or cold. More specifically, it is
defined as the rate at which heat or cold is transmitted through a
unit thickness of a material or gas in a direction normal to a
surface unit area due to the unit temperature gradient under steady
state conditions. One of the units thermal conductivity is measured
in is milli watts/meter Kelvin, mW/(m K). The heat transfer carrier
gas can be used in an indirect cooling process or direct cooling
process to enhance heat transfer rate. The heat transfer carrier
gas should be non-adsorbable or have minimal adsorbency on the
adsorbent such that parasitic loading is minimized or eliminated.
Additionally, the heat transfer carrier gas needs to be easily
separable from the main stream to be purified.
[0023] Known methods that utilize cold argon gas or cold liquid
argon experience parasitic loading of argon on the adsorbent, which
can greatly decrease the capacity of the adsorbent to remove the
oxygen impurity in an argon stream. "Air" or other process gas also
has the disadvantage of getting adsorbed onto the adsorbent and
decreasing the capacity of same. With helium's superior heat
conductivity, very low boiling temperature (-268.9.degree. C. or
4.25.degree. K), inert behavior and relatively non-adsorbing
property, it is particularly suitable to liquid phase separation
under TSA process. However, other inert gases that do not adsorb
onto the adsorbent and that exhibit favorable thermal conductivity
improvements can also be utilized as heat transfer carrier gas.
[0024] In one embodiment, the heat transfer carrier gas employed to
improve thermal conductivity should have a thermal conductivity
value greater than or equal to 2.0 mW/(m K) measured at a
temperature at 100K. In another embodiment the heat transfer
carrier gas should have a thermal conductivity value greater than
6.0 mW/(m K) as measured at 100K, in another embodiment greater
than 20 mW/(m K), in another embodiment greater than 30 mW/(m K),
in yet another embodiment greater than 50 mW/(m K), and in another
embodiment greater than 70 mW/(m K) as measured at 100K. Helium
with a thermal conductivity value of 75.5 mW/(m K) at 100K is a
preferred heat transfer carrier gas. Other non-limiting examples
include, but are not limited to, hydrogen, neon, krypton, xenon,
combinations and mixtures thereof, and the like. According to the
invention, the time consuming regeneration steps of a TSA process
can be significantly reduced allowing for the intensification of
the TSA process. The intensified TSA process and method of the
invention allows significant savings on both CAPEX and OPEX for a
given TSA process, particularly, for liquid phase separation
process operating under TSA mode.
[0025] A liquid cooling media generally employed to achieve
cryogenic temperatures is liquid nitrogen (LIN), although other
liquids can also be employed depending on cost and process
objectives. Non-limiting examples include liquid oxygen, neon,
hydrogen, helium, argon, and the like. Liquid nitrogen is a
preferred cooling media.
[0026] The process and system of the invention can also be applied
on gas phase separation/purification as long as there is an
economic way to separate the helium gas, or other heat transfer gas
employed to improve thermal conductivity, from the target gas
product. Although the invention can be used to purify any fluid by
the adsorptive removal of impurities from the fluid, it will be
described in detail with the purification of a liquid crude argon
stream by the removal of oxygen from the argon stream. The liquid
argon feed to the purification process of the invention can come
directly from distillation columns or from holding tanks. The
invention is not limited to liquid argon purification, and it can
be directly adapted to other liquid phase separation/purification.
For example, the process and system of the invention can be
usefully employed to purify a liquid nitrogen feed for the removal
of, for example, O.sub.2. Also, it can be usefully employed to
purify and enrich liquid xenon and/or krypton from oxygen feed, as
well as for the removal of, for example, N.sub.2O, CO.sub.2, and
THCs (total hydrocarbons). Additionally, the processes exemplified
in the Figures are only examples to illustrate embodiments of the
invention that utilize helium to enhance the heat transfer.
[0027] Argon is colorless, odorless, nontoxic as a solid, liquid,
or gas and is chemically inert under most conditions. As an inert
noble gas, it possesses special properties desirable for
applications related to the semi-conductor industry, lighting, and
other types of gas discharge tubes, welding and other
high-temperature industrial processes where ordinarily non-reactive
substances become reactive. Oxygen, in contrast to argon, is a
highly reactive substance (in gaseous or liquid form) and is often
a safety concern in that it supports combustion. Even low levels of
oxygen (<100 parts per million) are not acceptable for certain
laboratory and industrial processes. This also includes the
chemical processing industry where certain reactions must be
carried out primarily in the absence of oxygen. Successful
development of a cyclic adsorption process to achieve removal of
low concentrations (i.e., in the range of parts per million) of
oxygen from liquid argon, requires the identification of a suitable
adsorbent as well as the development and optimization of the
adsorption process steps. The purified liquid argon product should
contain at most 10 parts per million of oxygen, and preferably less
than or equal to 1 part per million of oxygen while the quantity of
oxygen in the liquid feed is usually between 10 and 50,000 parts
per million, in another embodiment 10-30,000 parts per million, and
in another embodiment 10-10,000 parts per million.
[0028] Production of liquid argon via cryogenic distillation is
well known and is the preferred method of producing high purity
argon. Cost considerations for the purification of argon have been
a driving influence in the development of special cryogenic systems
over at least several decades, and finding a suitable process which
is robust, reliable, and meets the economic criteria necessary for
customer demand has been sought.
[0029] Adsorption processes have also been described for the
purification of argon, however, these have in general been limited
to gas phase using 4A adsorbents and involved expensive energy
intensive adsorption processes. For example, considerable cost is
added to the adsorption process whenever an evacuation step is
required. The adsorption process step of regeneration that requires
vacuum has been historically very energy intensive in that vacuum
processing requires special equipment and other additional
peripherals leading to much higher energy demands as well as the
addition of undesirable but necessary capital and operating
expenses. The process of the present invention is generally
conducted at pressures of from about -5 psig to about 350 psig, in
another embodiment from about -5 to about 100 psig, in another
embodiment from about -5 to about 75 psig and in yet another
embodiment from about -5 to about 5 psig. The process of the
present invention represents a significant improvement over prior
art processes. The present invention contemplates two main
embodiments for intensifying a TSA process through utilization of a
heat transfer carrier gas. One employs indirect cooling of the
adsorbent bed in a helium environment wherein heat is removed
indirectly from the adsorbent bed primarily by a coolant, and the
other employs direct cooling of the adsorbent bed using a cold
helium stream. Various combinations of these embodiments are also
within the purview of the present invention.
1. Indirect Cooling with LIN in the Outer Jacket and Helium in the
Inner Adsorbent Vessel In this embodiment the process steps for
adsorptive LAR purification with indirect cooling are shown in FIG.
1. [0030] a) supplying liquid argon feed to the inlet of the
adsorption bed that contains oxygen in the concentration range of
about 1 to 10,000 parts per million, adsorbing at least part of the
oxygen on the adsorbent thereby producing a purified liquid argon
product leaving said adsorbent bed from the outlet with less than
or equal to 1 parts per million of oxygen; [0031] b) draining from
the outlet or inlet of said adsorbent bed residual liquid argon
while optionally supplying an argon purge stream at the inlet or
outlet of said adsorbent bed while maintaining the adsorbent bed at
temperature below 120 K; [0032] c) supplying a nitrogen purge at
the inlet or outlet of the adsorbent bed and allowing said
adsorbent bed containing said adsorbent to warm to a predetermined
temperature of at least 200 degrees Kelvin, preferably near ambient
temperature, desorbing at least part of the adsorbed oxygen and
removing this from the outlet or inlet of said adsorbent bed and;
[0033] d) supplying a gaseous helium purge of at least 200 degrees
Kelvin, preferably near ambient temperature, at the inlet or outlet
of the adsorbent bed, so that the gaseous effluent at the outlet or
inlet side of said adsorbent bed is predominantly helium and;
[0034] e) indirectly cooling said adsorbent bed containing
adsorbent, wherein said adsorbent is maintained under helium
environment at a predetermined pressure range of about -5 psig to
about 350 psig, preferably at a pressure range above ambient
pressure during the indirect cooling of said adsorbent, to a
temperature sufficient to sustain argon in liquid form; [0035] f)
wherein said process steps (a)-(e) are repeated in a cyclical
manner. Alternatively, indirect cooling to an intermediate
temperature approximately 150 K can be conducted under helium
atmosphere with liquid nitrogen as indirect coolant, followed by
directly cooling the adsorbent with liquid product. This is
exemplified by alternative steps e) and f), below. [0036] e)
indirectly cooling said adsorbent bed containing adsorbent and
having an inlet and an outlet and maintaining the adsorbent bed
under helium environment at a predetermined pressure range of about
-5 psig to about 350 psig, preferably at a pressure range above
ambient pressure during the indirect cooling of said adsorbent to a
temperature of less than about 150 degrees Kelvin using liquid
nitrogen; [0037] f) directly cooling said adsorbent bed with
purified liquid argon from the inlet or outlet of the adsorbent bed
to a temperature such that said adsorbent bed sustains an argon
feed in a liquid phase; [0038] g) wherein said process steps
(a)-(f) are repeated in a cyclical manner. The adsorbent vessel can
be a jacketed vessel or any other vessel capable of indirect
cooling. The adsorbent is located in the inner vessel and the
cooling media, i.e. liquid nitrogen, LIN, is circulated through the
outer vessel. The adsorbent is cooled down indirectly through the
jacket after the regeneration step and helium sweep step. During
the indirect cooling through jacket, helium is maintained in the
inner vessel for two main reasons: to enhance the heat transfer
process due to superior heat conductivity of helium and to maintain
positive pressure in the inner vessel to avoid the potential leaks.
Previous processes did not contemplate maintaining positive
pressure within the adsorbent vessel in order to mitigate vacuum
formation, which is detrimental for the heat transfer process and
increases the potential for leaks. 2. Direct Cooling with Helium to
the Adsorbent Vessel In this embodiment, the invention relates to a
direct helium cooling and warming method in a TSA process. This
approach does not require a jacketed vessel since direct contact
will be given to the cooling media, such as helium, with the
adsorbent. Cold gas helium is obtained through heat transfer with
LIN in a heat exchanger. A typical TSA process with direct helium
warming and cooling in accordance with the invention is illustrated
in FIG. 2a and comprises the following steps: [0039] a) supplying
liquid argon feed containing oxygen in the concentration range of
about 1 to 40,000 parts per million to the inlet of the adsorbent
bed, adsorbing at least part of the oxygen on the adsorbent thereby
producing a purified liquid argon product leaving said adsorbent
bed from the outlet with less than or equal to 1 parts per million
of oxygen; [0040] b) draining from the outlet or inlet of said
adsorbent bed residual liquid argon while optionally supplying an
argon purge at the inlet or outlet of said adsorbent bed while
maintaining the adsorbent bed at temperature below 120 K; [0041] c)
supplying a helium purge at the inlet or outlet of the adsorbent
bed and allowing said adsorbent bed containing said adsorbent to
warm to a predetermined temperature of at least 200 degrees Kelvin,
desorbing at least part of the adsorbed oxygen and removing this
from the inlet of said adsorbent bed, so that the gaseous effluent
at the outlet or inlet side of said adsorbent bed is predominantly
helium, the effluent helium gas is recycled to helium recovery
system to recover the helium and; [0042] d) directly cooling said
adsorbent bed containing adsorbent and having an inlet and an
outlet with cold helium to a temperature sufficient to cool said
adsorbent bed to a temperature sufficient to maintain argon in
liquid form, wherein said cold helium is maintained at a positive
pressure in said adsorbent vessel containing said adsorbent bed
during the direct cooling process; [0043] e) wherein said process
steps (a)-(d) are repeated in a cyclical manner. With liquid phase
separations, a drain step can be added after step a), to drain out
any liquid residues left inside the void space of the adsorbent
vessel.
[0044] Helium used in the TSA process of the invention can be
recycled to a purifier such as adsorptive, membrane or hybrid
system for recovery and reuse as shown in U.S. Pat. No. 7,294,172.
Depending on the cost of adding the helium recovery system,
modifications of the above cycles can be made to use warm nitrogen
or other gas stream as the purge gas to warm up the bed after drain
step and to use helium gas to sweep the nitrogen gas or other gas
stream out from the adsorbent bed before the cooling step. This
embodiment is shown in FIG. 2b wherein helium is used to sweep out
the nitrogen molecules left inside the adsorbent vessel. A summary
of the process steps follows. [0045] a) supplying from the inlet of
an adsorbent bed liquid argon feed that contains oxygen in the
concentration range of about 1 to 50,000 parts per million,
adsorbing at least part of the oxygen on the adsorbent thereby
producing a purified liquid argon product leaving said adsorbent
bed from the outlet with less than or equal to 1 parts per million
of oxygen; [0046] b) draining from the outlet or inlet of said
adsorbent bed residual liquid argon while optionally supplying an
argon purge at the inlet or outlet of said adsorbent bed while
maintaining the adsorbent bed at temperature below 120 K; [0047] c)
supplying a nitrogen purge at the inlet or outlet of the adsorbent
bed and allowing said adsorbent bed containing said adsorbent to
warm to a predetermined temperature of at least 200 degrees Kelvin,
desorbing at least part of the adsorbed oxygen and removing this
from the outlet or inlet of said adsorbent bed and; [0048] d)
supplying a gaseous helium purge of at least 200 degrees Kelvin at
the inlet or outlet of the adsorbent bed, so that the gaseous
effluent at the outlet or inlet side of said adsorbent bed is
predominantly helium and; [0049] e) directly cooling said adsorbent
bed containing adsorbent and having an inlet and an outlet with
cold helium, to a temperature of 120 K or as low as liquid argon
temperature; [0050] f) wherein said process steps (a)-(f) are
repeated in a cyclical manner. The helium sweep can be vented out
to atmosphere or it can be recovered if a recovery system is
available. The cold helium in step (e) above can be provided by
indirectly cooling a helium stream in closed loop against liquid
nitrogen or nitrogen vapor or both. The closed loop circuit can be
configured to have purge capability to prevent build-up of
undesirable components in the circulating helium stream, as well as
provisions for make-up helium. Additionally cold helium can be
provided at a constant temperature during the entire direct cooling
of said adsorbent bed, or at progressively colder temperatures.
[0051] The direct cooling method does not require a jacketed
vessel, CAPEX savings. More specifically, indirect cooling with a
jacketed vessel constrains the choice of adsorbent vessel diameter.
With direct cooling, vessel diameter is not limited allowing for
more capacity for oxygen removal. Additionally, the cooling process
can be intensified from mainly heat conduction to heat
convection.
[0052] The flow direction in either embodiment is not limiting and
the feed flow can be any direction, i.e., from the top or the
bottom sides or any of the sides of the adsorbent vessel.
Additionally, the direct inert gas/helium warm and cool flow to the
adsorbent bed is not limited to countercurrent flow and can be any
direction as desired. The TSA process of the invention is not
limited to 2-bed system. It can be one bed system with buffer tank
to temporally store the crude during the time the bed is in
regeneration, or it can be a multi-bed system with 2 or more beds.
In one embodiment, the process is continuous and, therefore, the
system requires at least two adsorbent beds; one of which
carries-out the adsorption or purification step while another bed
is being regenerated in preparation for a further adsorption or
purification step. The choice of the number of beds required to
keep the system operational and efficient is not limited and is
dictated by system installation and process requirements and/or
dictated by customer or application needs.
[0053] Regardless whether direct and/or indirect cooling is
employed, the process of the invention includes several distinct
steps which are operated in sequence and repeated in a cyclical
manner. Those steps are described in more detail below.
Purification or Adsorption Step
[0054] Impure (oxygen containing) cryogenic liquid argon is
contacted with adsorbent during the purification or adsorption
step, whereupon the oxygen impurities are substantially adsorbed by
the adsorbent and a purified liquid argon product is obtained. The
purification step takes place at or below critical cryogenic
temperatures to ensure the liquid state of argon feed persists at
pressures in the range of 20-150 psig. However, purification at
pressures higher than 150 psig, caused by a hydrostatic head
pressure gain or pressurization of the feed using rotating
equipment or a combination thereof, is an alternative way of
practicing this invention. The oxygen level in the impure cryogenic
liquid argon feed can range from as low as 10 parts per million to
one or more thousand parts per million (preferably not more than
50,000 parts per million). The liquid argon feed is introduced at
the top or bottom of the adsorbent bed. The purified liquid argon,
collected at the bottom or top of the bed, is then subsequently
sent to a holding product tank. The purification step is completed
once the oxygen level in the liquid argon product reaches the
desirable purification level of less than or equal to 10 parts per
million and preferably less than or equal to 1 part per million of
oxygen in argon.
Draining Step
[0055] Next, the bed is drained to eliminate the liquid contained
in the adsorbent bed prior to regeneration through the help of
displacement gases. Exemplary examples of displacement gases that
can be utilized include nitrogen, argon, helium, and purified air.
After the draining of any residual cryogenic liquid is completed,
the regeneration step can be initiated.
Regeneration
[0056] The bulk of the oxygen impurity adsorbed in the adsorbent is
removed by increasing the temperature of the adsorbent and using a
suitable purge gas. During this step, the temperature of the
adsorbent bed increases as it is directly contacted with the purge
gas until the bed temperature reaches at least 200 degrees Kelvin
and more preferably around ambient temperature. Exemplary purge
gases for the regeneration include nitrogen, argon, helium,
purified air or mixtures of two or more of same. Nitrogen is a
preferred purge gas for regeneration. In cases where nitrogen
and/or argon are less readily available other gases can be used to
purge the adsorbent bed and regenerate the adsorbent including
mixtures of dry carbon dioxide and hydrocarbon free air or a
mixture of nitrogen and oxygen. Regardless of the purge gas chosen,
it should be moisture free. In one embodiment, the bed can be
initially purged with nitrogen followed by an argon purge. In
another embodiment helium is utilized after the initial nitrogen
purge instead of argon. In another embodiment, helium is employed
as the sole purge gas to warm the adsorbent bed. The helium can be
a fresh supply or it can be recycled and purified helium from the
indirect cooling step. The temperature of the purge gas is at least
200 degrees Kelvin and more preferably near ambient temperature,
while the pressure is at least 2 psig and more preferably at least
15 psig. The temperature of the purge gas could be higher than
ambient temperature, with the proviso that the porous adsorbent has
enough thermal stability to withstand a higher temperature
purge.
[0057] In another embodiment, the purge gas is introduced from the
outlet portion towards the inlet portion of the bed, in a direction
countercurrent to the liquid feed stream. Purging the bed from the
inlet to the outlet portion, in the same direction as the flow of
the liquid to be purified are alternative embodiments which can
accomplish similar results, with the proviso that the bed is below
the fluidization limit or that the adsorbent and the bed is fully
contained.
Indirect Cooling
[0058] At the end of the regeneration step, the adsorbent bed
reaches a temperature of at least 200 degrees Kelvin, and more
preferably around ambient temperature. To proceed to the next
purification cycle, the bed needs to be cooled to a temperature
below the argon boiling point. One way to achieve this is via
indirect cooling, i.e. by flowing liquid nitrogen (at a pressure
ranging from about 18-30 psig) or cold gaseous nitrogen or liquid
argon or other cooling media through a jacket surrounding the
adsorbent vessel until the bed temperature, as measured at the
center of the bed, has reached the preferred temperature. The
adsorbent vessel is designed based on the indirect cooling time for
a specific vessel diameter to ensure heat transfer from the jacket
to the inner of adsorbent bed. Indirect cooling of the adsorbent
bed to a specified temperature, at least about 150K, prior to
bringing the cryogenic liquid in direct contact with the adsorbent
is critical to control the micro structure of the adsorbent and
ensure that the capacity of the bed to remove O.sub.2 is maximized.
As previously mentioned, the poor heat conductivity of adsorbent
material generally constrains the process cycle time, adsorbent
vessel diameter and restricts process intensification.
[0059] The present inventors have discovered that the thermal
conductivity during the indirect cooling step can be dramatically
increased by introducing helium into the adsorbent vessel as
described herein. More specifically, after the warm purge of the
adsorbent bed, any residual gas molecule from the purge step can be
swept out with a helium sweep. If helium is utilized as the sole
purge gas, the helium sweep step can obviously be omitted. A helium
recovery system can be added to recover helium from the waste
effluent. Once the adsorbent is free from residual gas molecules,
helium gas is introduced to the adsorbent vessel at just above
ambient pressure (.about.5 psig) to fill in the void space of the
adsorbent bed. Introducing helium in order to fill the void space
and maintaining same during the indirect cooling step not only
improves thermal conductivity, it also reduces the risk of leaking
due to vacuum since positive pressure is maintained in the
adsorbent vessel.
[0060] After helium is added to the adsorbent bed in an amount
sufficient to maintain a positive pressure inside the bed (.about.5
psig) or simultaneous with the addition of helium, indirect cooling
is initiated by sending liquid nitrogen or other cooling media to
the jacket surrounding the adsorbent bed. A circulating media could
be used to create a flow of helium with minimum helium consumption
and better heat transfer effect to take the advantages of both
indirect and direct cooling. Because helium will not condense and
adsorption is minimal at the process temperature (.about.90K), the
helium is in vapor phase and naturally separates from liquid argon
product, and can be vented from the top of the liquid argon storage
tank. Helium consumption is dependent on the void space of the
vessel and piping before or after the valves up or down stream.
Introducing helium in the adsorbent vessel in this fashion improves
the heat conductivity during the indirect cooling step by a factor
of up to 10. This dramatic improvement in heat transfer time
significantly reduces the time necessary for cooling down from
ambient temperatures to cryogenic temperatures during the indirect
cooling step. The helium used can be recovered, recycled and
purified to remove any impurities for next continuous usage.
Direct Cooling
[0061] During the direct cooling step, the bed is cooled to
approximately 90 degrees Kelvin by flowing liquid argon directly
through the bed. This liquid argon stream could either be obtained
from the impure liquid argon feed or from a portion of the purified
liquid argon product, depending on the choice of design of the
process. The subsequent purification step can be initiated once the
bed has reached a temperature of 90 degrees Kelvin. With helium
enhanced heat transfer during the indirect cooling step, it is
possible, and in some situations preferable to indirectly cool the
adsorbent bed all the way to the process temperature around 90
degrees Kelvin and minimize or eliminate direct cooling with liquid
argon product entirely.
[0062] Alternatively, indirect cooling can be omitted entirely and
the cold helium can be employed as the cooling media to directly
cool the adsorbent. More specifically, warm helium is first sent
directly to the adsorbent bed to warm up the adsorbent and purge
out the adsorbate and release the adsorbent capacity. Then cold
helium is sent directly to the adsorbent to cool down the adsorbent
to the separation process temperature for next cycle.
[0063] It should be understood that the process described above
often will include two or more adsorbent beds, wherein the process
for purifying liquid argon in each bed is offset from one another.
Specifically, for instance, when one adsorbent bed is being
provided feed gas, a second adsorbent bed can be regenerating. If
the process utilizes four beds then the third adsorbent bed may be
idle, and the fourth adsorbent bed may be cooling.
[0064] The development of a preferred cyclic cryogenic adsorption
process depends to a high degree on the ability to warm and cool
the adsorbent bed within a specified and optimal time period. It
will be understood by those skilled in the art that for a two-bed
process, the time to drain the adsorbent bed and the heating (for
adsorbent regeneration) and cooling time period also provides a key
process variable and time frame for the "on-line time" of each
adsorbent bed. Furthermore, it is desirable from a process and
economics standpoint to not cycle each bed very frequently. The
preferable online time requirement for each bed is at least 3 hours
and more preferably, from around one to seven days, depending on
the plant and vessel designs and the adsorbent chosen.
[0065] In one embodiment the present invention relates to a TSA
process that can be beneficially applied to argon purification
processes for removing oxygen from liquid argon. The process
generally comprises the following cyclical steps:
[0066] a) supplying the adsorbent bed with the liquid argon feed
that contains oxygen, thereby producing a purified liquid argon
product leaving the adsorbent bed with less oxygen than existing in
the liquid argon feed;
[0067] b) draining the residual liquid argon and removing this
residual out of the bed and;
[0068] c) allowing the adsorbent bed holding the adsorbent to warm
to a temperature such that the adsorbent is regenerated to the
point that the adsorbent bed can continue to remove the oxygen and
continue to provide the purified liquid argon once the adsorbent
bed is cooled down as described in step (d) below;
[0069] d) introducing helium to the adsorbent bed in an amount to
substantially fill the void space of the bed and maintaining same
during the indirect cooling step;
[0070] e) cooling an adsorbent bed holding adsorbent to a
temperature such that the adsorbent bed sustains an argon feed in a
liquid phase.
[0071] The process described above is a cycle operated in a fashion
comprising steps (a)-(e) where the cycle is repeated, as needed,
and the adsorbent bed contains zeolite adsorbents of either the 4A
type zeolites or ion exchanged 4A type zeolites or both and where
the ion exchange is accomplished with lithium ions. The adsorbents
contained within the adsorbent beds are effectively regenerated to
remove oxygen via desorption by warming the beds with various gases
(e.g., nitrogen, argon or gas mixtures including purified air) at
temperatures that may reach ambient conditions.
[0072] In another embodiment, the adsorption process for removing
oxygen from liquid argon is described as follows:
[0073] a) supplying from the inlet of an adsorbent bed the liquid
argon feed that contains oxygen in the concentration range of about
10 to 40,000 parts per million, adsorbing at least part of the
oxygen on the adsorbent thereby producing a purified liquid argon
product leaving the adsorbent bed from the outlet with less than or
equal to 1 parts per million of oxygen;
[0074] b) supplying a nitrogen purge at the inlet or outlet of the
adsorbent bed and draining from the outlet or inlet of the
adsorbent bed residual liquid argon and;
[0075] c) continuing the nitrogen purge at the inlet or outlet of
the adsorbent bed and allowing the adsorbent bed containing the
adsorbent to warm to a temperature of at least 200 degrees Kelvin,
desorbing at least part of the adsorbed oxygen and removing this
from the outlet or inlet of the adsorbent bed and;
[0076] d) supplying a gaseous purge of argon and/or helium at a
temperature of least 200 degrees Kelvin at the inlet or outlet of
the adsorbent bed, so that the gaseous effluent at the outlet or
inlet side of the adsorbent bed is predominantly argon and/or
helium;
[0077] e) introducing helium to the adsorbent bed in an amount to
substantially fill the void space of the bed and maintaining helium
in the bed during the indirect cooling step;
[0078] f) indirectly cooling the adsorbent bed containing
adsorbent, where the bed has an inlet and an outlet, as well as a
direct and an indirect cooling means to a temperature below about
150 degrees Kelvin and;
[0079] g) directly cooling the adsorbent bed with liquid argon to a
temperature such that the adsorbent bed sustains an argon feed in a
liquid phase;
[0080] h) the process steps (a)-(g) are repeated in a cyclical
manner.
[0081] The liquid argon utilized in the direct cooling step may be
either a purified liquid argon stream or the crude liquid argon
feed stream.
[0082] In another embodiment, the adsorption process for removing
oxygen from liquid argon is described as follows:
[0083] a) supplying from the inlet of an adsorbent bed the liquid
argon feed that contains oxygen in the concentration range of about
10 to 40,000 parts per million, adsorbing at least part of the
oxygen on the adsorbent thereby producing a purified liquid argon
product leaving the adsorbent bed from the outlet with less than or
equal to 1 parts per million of oxygen;
[0084] b) supplying a helium purge at the inlet or outlet of the
adsorbent bed and draining from the outlet or inlet of the
adsorbent bed purified residual liquid argon and;
[0085] c) continuing the helium purge at the inlet or outlet of the
adsorbent bed and allowing the adsorbent bed containing the
adsorbent to warm to a temperature of at least 200 degrees Kelvin,
desorbing at least part of the adsorbed oxygen and removing this
from the outlet or inlet of the adsorbent bed, so that the gaseous
effluent at the inlet side of the adsorbent bed is helium and;
[0086] d) introducing cold helium to the adsorbent bed to directly
cool down the adsorbent to the separation process temperature for
next cycle, i.e., such that the adsorbent bed sustains an argon
feed in a liquid phase. Process steps (a)-(d) are repeated in a
cyclical manner.
[0087] The economic advantages provided by the current invention
include the reduction of capital cost of more conventional
alternative technologies aimed at purifying liquid argon from
oxygen impurities by use of adsorption processes. This reduction in
capital cost is a result of the combination of an economically
attractive adsorption process cycle, especially as it pertains to
the regeneration step (e.g., elimination of any vacuum regeneration
step), the use of helium to improve thermal conductivity during the
indirect cooling step, and the use of a synthetic zeolite material
that does not require expensive reducing agents (e.g., hydrogen) to
be regenerated.
[0088] Although there are alternative process methodologies that
could be used to practice the present invention, one preferred
embodiment is discussed below, with reference to the FIG. 3. For
purposes of explanation and simplicity, the use of a single
adsorbent bed is described and shown in the FIG. 3. However, it
will be understood by those skilled in the art, that the process
described is applicable to processes that utilize two or more
beds.
[0089] FIG. 3 describes the consecutive steps for a cyclic TSA
process for LAR purification in accordance with the present
invention. In the initial stage of set-up, the adsorbent bed (100)
is tightly packed with adsorbent material (200). External cooling
with liquid nitrogen or other cooling media is provided via a
cooling jacket (300) that surrounds the bed. Stage (A) depicts the
initial set-up arrangement prior to the beginning of purification,
where the adsorbent bed is at about 90 degrees Kelvin. Stage (B)
illustrates the purification step of the adsorption process. During
Stage (B), the liquid argon stream containing oxygen is fed into
the adsorbent bed as represented by the arrow (1). The feed is
provided at either the bottom or the top of the bed. This feed
stream (1) is liquid phase argon that contains oxygen impurities in
the range of 10 to 10,000 parts per million of oxygen. The pressure
within the bed during the introduction of the liquid argon feed is
about 60 psig and the corresponding temperature for this exemplary
embodiment ensured that the argon feed remained in the liquid phase
at the respective process pressure conditions, namely a temperature
of about 90 degrees Kelvin. The adsorbent is selected so that under
the purification conditions, the absorbent is selective for oxygen.
The liquid argon product stream (2) is collected at the top end or
the bottom end of the bed. The purification step is completed once
the level of oxygen in the liquid argon product reaches a
concentration of 1 part per million. At this instance, the online
bed should be prepared for regeneration and the second bed is
brought online to perform the purification.
[0090] Prior to regeneration of the adsorbent, the liquid argon
volume in the bed is drained as shown in Stage (C) at cryogenic
temperature while maintaining liquid nitrogen in the cooling
jacket. In order to ensure that the bed is drained properly and in
a timely fashion, a cold purge step is provided using an inert
displacement gas (normally argon or nitrogen) denoted as stream
(3). The temperature of the displacement gas is about 90-150
degrees Kelvin, preferably 90-120 degrees Kelvin, while its
pressure is preferably about 15 psig. The draining step is
completed once all the liquid that was contained in the adsorbent
bed is drained. The liquid drain stream (4), as provided and shown,
is rich in liquid argon that remained contaminated with oxygen and
collected at the bottom of the bed and can optionally be recycled.
After adsorbent bed drain is completed, the liquid nitrogen is also
drained from the cooling jacket and vented to the atmosphere.
[0091] After bed (100) is drained, the adsorbent is regenerated
using a warm purge gas while the adsorbent remains within the same
bed (100). As illustrated in Stages (D) and (E), a nitrogen purge
through the bed is initiated in a concurrent or countercurrent
fashion in relation to the feed (i.e. from the top portion to the
bottom portion of the bed). The temperature and pressure of the
nitrogen purge gas, stream (5) and (7), is about 300 degrees Kelvin
and 15 psig, respectively. The effluent during the purge Stage (D),
indicated as stream (6), is predominantly composed of undesirable
oxygen contaminant, and some argon in the nitrogen purge gas.
During this step, oxygen is desorbed from the zeolite adsorbent and
some quantity of argon is desorbed as the temperature within the
adsorbent bed rises. As the purging continues, and the bed
temperature approaches the temperature of the purge gas (shown as
nitrogen in stream (7)), the gaseous effluent, stream (8), becomes
predominantly nitrogen (Stage (E)). The nitrogen purge is completed
when the bed temperature reaches about 300 degrees Kelvin. At that
point, the zeolite becomes loaded with nitrogen. For optimum
performance most of the available sites of the adsorbent must be
free and capable of capturing a majority of oxygen impurities.
Hence, subsequent to the nitrogen gas purge, an argon gas or helium
gas purge, indicated by the stream (9) shown, is initiated (Stage
(F)). The temperature of the gaseous purge, whether argon or
helium, is about 300 degrees Kelvin, while the pressure is around
15 psig. This is a very important step in the regeneration of the
adsorption scheme. During the last part of the regeneration step,
(Stage (F)), a gaseous effluent of comprising nitrogen and argon or
helium exits the bed (100), indicated by stream (10). The argon or
helium gas purge is completed when the effluent, stream (10) is
predominantly argon or helium gas, depending of course on the purge
gas utilized. At this instance, the argon (or helium) gas occupies
the macropore space of the adsorbent particles as well as the void
space between particles within the adsorbent bed. In one
embodiment, helium is purge gas employed after purging with
nitrogen.
[0092] After the argon and/or helium gas purge is completed, helium
gas is introduced to the adsorbent vessel at just above ambient
pressure (.about.5 psig) to fill in the void space of the adsorbent
bed. It is preferred that positive pressure be maintained within
the vessel during the entire indirect cooling step in order to
minimize the risk of leaking. Indirect cooling of the adsorbent bed
can then be initiated.
[0093] Cooling the adsorbent begins in Stage (G). During this
stage, indirect heat transfer from a liquid nitrogen medium flowing
in a jacket (300) surrounding the bed (100) cooled the adsorbent
bed to approximately 120 degrees Kelvin. The pressure of the liquid
nitrogen in the jacket is regulated so that the liquid nitrogen
temperature is above the melting point of argon at the process
conditions and below the saturation point of nitrogen. Once the
temperature in the middle of the adsorbent bed is about 120 degrees
Kelvin, the direct cooling step is initiated, as shown in Stage
(H). This involves direct contact of the adsorbent material (200)
with a purified liquid argon stream denoted stream (11). Stream
(11) is introduced at the top or bottom of the adsorbent bed and it
cools the bed to the desired temperature for purification of about
90 degrees Kelvin. This also facilitates building a liquid head to
fill the adsorbent bed with purified liquid argon. At the end of
this step the temperature at the middle of the bed is about 90
degrees Kelvin and the pressure is around 60 psig. Preferably, the
adsorbent bed (100) can be indirectly cooled to about 90 degrees
Kelvin under helium environment, and direct cooling with purified
liquid argon stream is avoided. This allows for the next
purification cycle to begin again at Stage (B).
[0094] Adding helium to the adsorbent vessel prior to the indirect
cooling step significantly improves heat transfer and reduces risk
of piping leaks. More particularly, the helium dramatically
improves thermal conductivity during the indirect cooling step
which significantly reduces the heat transfer time needed during
cooling down from ambient temperature to cryogenic temperature.
This enables process intensification for reducing vessel size and
hence capital costs. Utilizing helium also reduces the risk of
leakage and improves the overall reliability of the operation. More
specifically, valves are located at several different locations up
or down stream of the adsorbent vessel. Those valves as well as
other connections are potential leak points during the indirect
cooling period in processes which create a vacuum inside the
adsorbent bed. Any leak into the adsorbent bed will detrimentally
affect the O.sub.2 capacity on the adsorbent, therefore reduce or
even terminate the performance in terms of O.sub.2 removal from
LAR. Maintaining a helium atmosphere in the vessel during the
indirect cooling step, protects the adsorbent from leaks and air
infiltration, reduces the risk of adsorbent contamination, and
increase the process reliability from an operations standing point.
Additionally, because a vacuum is not created, the need for special
equipment and peripherals is eliminated and operating expenses are
reduced.
[0095] In one embodiment a full TSA purification cycle according to
the invention comprises:
[0096] (i) providing the adsorbent bed with either virgin or
regenerated adsorbent--Stage (A)
[0097] (ii) purification of the liquid argon feed providing
purified liquid argon product--Stage (B)
[0098] (ii) drainage of the liquid argon contained in the bed at
the end of purification step--Stage (C)
[0099] (iii) regeneration of the adsorbent via warm-up--Stages (D),
(E), and (F) and;
[0100] (iv) adding helium gas to the adsorbent vessel followed by
cool-down of the adsorbent bed--Stages (G) and (H) so that the
cycle can be repeated.
[0101] The adsorbent is chosen depending on the liquid stream to be
purified and the impurity that is to be removed. If argon is the
feed to be purified, the proper adsorbent which will adsorb, at
most, very small amounts of argon. The ideal adsorbent does not
adsorb any argon and also removes impurities from the argon which
are predominantly oxygen impurities. However, in practice, the
adsorbents that have been used still have some argon uptake
capacity. Herein are described adsorbents specifically designed to
minimize argon uptake.
[0102] U.S. patent application 2014/0249023, which is incorporated
herein by reference describes adsorbents for purification of liquid
argon. The adsorbents preferred for the present invention are
primarily beads (with predominantly spherical particle geometry)
with an average particle size of less than or equal to 2.0 mm and
more preferably less than or equal to 1.0 mm. Additionally, the
desired adsorbents have a porosity that is in a range of between 33
and 40 percent as measured by mercury (Hg) porosimetry. A binder is
used to formulate the beaded absorbent, such that the binder is
present at no greater than 15 weight percent. This binder is
preferably purified versions of attapulgite, halloysite, sepiolite
or mixtures thereof.
[0103] Testing to establish the viability of this purification
cycle was performed in a pilot plant which included an adsorbent
bed with a tube-in-tube type cooling system. The inner tube, which
had an outside diameter of one inch, was packed with the adsorbent.
The outer jacket was utilized for passive cooling. The length of
the bed was either one foot or three feet. This bed allowed for
receiving cryogenic liquid flow into an inlet section and the
delivery of a cryogenic liquid product at the outlet. The bed was
regenerated on-line as is described above.
[0104] Compared with previously proposed indirect cooling TSA
processes for liquid argon purification, the present invention
alleviates many of the restrictions on the adsorbent vessel design
in terms of vessel diameter. The claimed method can also
accommodate increased feed flowrates and/or higher O.sub.2 impurity
levels in crude argon feed and enables TSA process intensification,
i.e., a smaller vessel can be utilized due to a more rapid process
cycle.
The invention will now be illustrated by the following non-limiting
examples.
Example 1
[0105] As shown in FIG. 4, an experimental system was set up to
measure the indirect cooling down temperatures vs. time at
different conditions. A 5.3'' ID vessel packed with 4A zeolite
adsorbent materials was embedded with thermocouples at three
different locations (top, middle and bottom) as illustrated in FIG.
4. Those thermocouples were positioned in the center of each
location. A pressure transducer was placed inside the adsorbent
vessel to measure the pressure changes during the adsorbent
indirect cooling process. For comparison, the temperature decrease
with time during the indirect cooling process from ambient
temperature to around 100 Kelvin was measured and recorded under
both vacuum environment and helium environment. The measured
temperatures (center of the adsorbent vessel T2 vs. time results
were recoded and reproduced in FIG. 5. The results indicated that
for a 5.3 inches ID adsorbent vessel, cooling down the adsorbent
from ambient to about 100 Kelvin under vacuum condition (0.04 psia)
will take 23.5 hours; however, this cooling down process with
helium filled the adsorbent vessel will only take about 1.5 hours,
which reduced the cooling down time roughly 15 times. This result
matches the simulation results shown in FIG. 6 which indicate
similar indirect cooling time reduction for adsorbent vessel at
different diameters.
[0106] FIG. 6 compares simulation results of cooling down times for
adsorbent vessels of 13.5 inches ID and 17.5 inches ID with the
technology of the present invention vs. prior designs that do not
utilize a helium atmosphere in the adsorbent vessel. As the data
show, the cooling time in the indirect cooling step is
significantly reduced compared to prior designs that do not utilize
a helium atmosphere in the adsorbent vessel. The curves in FIG. 6
are parametric in heat conductivity relative to baseline (vacuum)
with the faster cool down curve representing a factor of 10
increase in thermal conductivity (Keff=0.55 W/m/K) versus vacuum
(Keff=0.055 W/m/K). For example, as shown in FIG. 6, the cooling
down time from 300 K to 90 K for a 13.5 inches ID vessel is reduced
from over 90 hours to less than 20 hours. This significantly
reduces liquid nitrogen consumption and dramatically improves
process efficiency in that the data suggest that utilizing helium
during the indirect cooling step can reduce the cycle time by 50%
or more, allowing one to reduce vessel size and/or increase flow
rate.
[0107] As the data demonstrate, utilizing helium in the direct
cooling and warming step significantly reduces the heat transfer
time needed during warm regeneration and pre-cooling, enabling
process intensification for reducing vessel size and capital
savings.
[0108] As described previously in U.S. patent application
2014/0245782, which is incorporated herein by reference, the intent
of integrating adsorptive LAR purification technology into
distillation process as a hybrid method of producing product argon
is to optimize the overall argon production economics. The overall
coldbox space is drastically reduced due to superstaged column
reduction and the oxygen impurities left will be removed through
using adsorptive system. For a designed productivity ASU plants
with integrated adsorptive LAR purification process, it is
desirable to minimize the size of the overall hybrid system by
reducing both sizes of superstaged distillation column and
adsorptive system. Given a fixed production rate of ASU, the less
the oxygen impurity the superstaged column needs to remove, the
more coldbox space will be saved. On the other hand, the higher
oxygen impurity the adsorptive system has to remove, the bigger the
adsorptive system will need to be. For those who are familiar with
the art, it is desirable to minimize the relative high unit cost of
the coldbox, and maximize the adsorptive system capacity for oxygen
removal. Therefore, it is desirable to minimize adsorptive system
so as to keep the adsorptive LAR purification system capital and
operation cost minimal.
[0109] The size of the adsorptive LAR purification system depends
on key process parameters such as crude argon feed flow to the
adsorptive system, oxygen impurity level within the crude argon
feed, adsorbent bed on stream time to make argon product and
cooling method in the TSA process. Any intensification of the
process is almost always beneficial from capital standpoint.
[0110] Table 1 compares some adsorptive LAR purification system
under various process conditions. Two types of plants are
illustrated here. One is an intermediate ASU plant with crude LAR
flow at 32 KCFH to the adsorptive system (Plant 1), and the other
one is a large ASU plant with crude LAR flow at 52 KCFH to the
adsorptive system (Plant 2). Various oxygen impurity levels (1000
and 40,000 ppmv) are considered to be removed in the adsorptive LAR
purification system. From Table 1, it can be seen that, if indirect
cooling under vacuum is applied in the TSA process, according to
heat transfer modeling results shown in FIG. 6, the maximum
adsorbent vessel diameter is limited to around 13.5 in. (maximum
diameter for indirectly cool down the adsorbent in 2 days), the
cooling down time is estimated for more than 1 day to reach less
than 150 degree Kelvin before product LAR can be used to directly
cool down the adsorbent further to around 90 degree Kelvin as shown
in the process in US patent application 2014/0245781. Therefore the
entire regeneration time is estimated at 2 days (drain+warm
purge+cooling). Those requirements set the adsorbent vessel length
at 15 ft. However, with indirect cooling under helium for enhancing
the heat transfer according to the present invention, the cycle
time can be dramatically reduced. If the bed on stream time is cut
from 2 day to 1 day, the vessel length is reduced to half, enabling
significant capital savings on adsorbent vessels and process
design.
[0111] To further reduce the superstaged column coldbox space, if
high oxygen impurity at 40,000 ppmv is sent to the adsorptive
system, from results shown in Table 1, it can be seen that it will
be impractical to use adsorptive LAR purification system to
completely remove the oxygen impurity to product grade due to the
length of the adsorbent vessel needed, i.e., approximately over 84
ft. However, using direct cooling according to this invention,
adsorbent vessel diameter can be increased to around 6 ft. allowing
the vessel length to be reduced down to about 15 ft.
[0112] For larger plants such as plant 2, with high crude argon
feed flowrates to the adsorbent vessel and oxygen impurity level of
1000 pm in the feed, the indirect cooling with helium method of
this invention enables one to reduce vessel length to one third,
compared with the case of indirect cooling under vacuum. This is
because the indirect cooling time under helium is much faster than
the case of under vacuum as shown in FIG. 6. So the TSA process is
significantly intensified by reducing the time limiting step, i.e.
the indirect cooling step. In larger plants such as plant 2 with
high crude argon feed flows to the adsorbent vessel, and oxygen
impurity levels at 40000 pm in the feed, previous methods with
indirect cooling under vacuum are impractical due to the length of
the adsorbent vessel needed, i.e., approximately over 813 ft. Even
with indirect cooling under helium with cooling down time less than
10 hours, still has the limitation of vessel diameter at 17.5 in.
as indicated in FIG. 6, which will lead to impractical vessel
length of 136 ft. If direct cooling according to the present
invention is used, the adsorbent vessel diameter limitation is
removed due to the heat transfer in cooling process change from
heat conduction to heat convection. Therefore the vessel diameter
can be increased freely to around 6 ft. for example, allowing the
vessel length to be reduced down to about 24 ft.
TABLE-US-00001 TABLE 1 Comparison of adsorbent vessel sizing with
different TSA process Plant 1 Plant 2 Feed Flowrate 32 52 (KCFH,
NTP) O2 Impurity 1,000 40,000 1,000 40,000 (ppmv) TSA Indirect
Indirect Indirect Indirect Direct Indirect Indirect Indirect
Indirect Direct Cooling cooling cooling cooling cooling cooling
cooling cooling cooling cooling cooling method (under (under (under
(under (under (under (under (under (under (under vacuum) helium)
vacuum) helium) helium) vacuum) helium) vacuum) helium) helium) Bed
on Stream 2 1 2 0.5 1 3 1 3 0.5 1 Time (day) Vessel ID (in) 13.5
13.5 13.5 17.5 59 17.5 17.5 17.5 17.5 59 Vessel Length 20 10 563 84
15 29 10 813 136 24 (ft)
[0113] Also, with more rapid cycle, the argon parasitic loading on
the adsorbent materials becomes negligible due to slow argon uptake
rate on the adsorbent. This allows for conventional 4A zeolite
(NaA) to be used as the adsorbent materials instead of more
expensive lithium exchanged 4A adsorbents required by many known
processes.
[0114] Various modifications and changes may be made with respect
to the foregoing detailed description and certain embodiments of
the invention will become apparent to those skilled in the art,
without departing from the spirit of the present disclosure.
* * * * *